Its called xbox live stealth this (should keep ur jtag under the radar longer from xbox live to detecting you having a modified console online) and banning it, there is multyple services around.
Not all as good as the others ones but yea im saving up money to go with the original creators from stealth to be sure but they are the most expensive too prices are to be requested by them i cant tell out off my head but yea ill link to these services the 2 best in my opinion.
U will have more costs tho when u get banned for example ull need a new kv.bin file (file that microsoft uses to bann u) wich people sell for around the 10 to 15$ most of the time, also gold becouse some xbls have gold spoof (fake gold) but it doesnt work on newer games like gta 5 online... so u will still need real gold on ur account for some games if u have gold spoof in the service.
i try to use trials as much as possible like 2 day trial code 1 week gold code cuz sometimes u get banned fast so sucks if u payed for 1 year gold if u lose it after 2 weeks
-XBLS Service 1
-XBLS Service 2